The field of the invention is laser-based alignment equipment, and particularly, systems which produce an alignment field using a laser transmitter and one or more receivers which detect the alignment field and provide an accurate alignment indication at locations remote from the laser transmitter.
In prior laser-based alignment systems, such as that disclosed in U.S. Pat. No. 3,588,249, for example, a reference plane is established throughout a work site by a transmitter which emits laser energy in a level reference plane. This reference plane is typically established by a beam which is projected radially outward from the transmitter and rotated continuously through 360 degrees to sweep around the entire work site. One or more receivers may be employed throughout the Work site to sense the location of this reference plane. Such receivers may be employed as part of a surveyor rod as described in U.S. Pat. No. 4,030,832, or they may be employed as part of a control system on construction or agricultural equipment as described in U.S. Pat. Nos. 3,813,171; 3,873,226; 3,997,071; and 4,034,490.
Prior laser alignment systems provide an indication of elevation throughout the work site, but they do not indicate the position of the receiver within the work site. Thus, for example, the blade on a load grader can be automatically controlled to a desired elevation by such prior systems, but it is up to the operator to determine where the road grader is located and what the elevation should be at that location.
In other words, prior laser alignment systems provide only one dimension of position information-elevation.